1. Field of the Invention
The present invention relates to an automatic centering controller for aligning the axis of a tool spindle of, preferably, a numerically controlled machine tool with the axis of a reference circumferential surface of an article mounted on the machine tool.
2. Description of the Prior Art
In performing a boring operation on a prior numerically controlled machine tool, a tool spindle of the machine tool must be positioned precisely in axial alignment with the axis of a preliminary bore to be machined or of a reference bore in accordance with a numerical control program. Such positioning of the tool spindle, however, invites a deviation of the axis of the tool spindle from the axis of the preliminary or reference bore due to errors which are unavoidably involved in machining the preliminary bore in a preceding step and in setting up a workpiece or a workpiece pallet on the machine tool, and precise alignment of the tool spindle with the preliminary or reference bore is, therefore, hardly attained. For this reason, prior to a boring machining, an operator has to discontinue the tape mode operation of the machine tool, then manually detect the center of a preliminary or reference bore and return the machine tool to the tape mode operation. Such operator's manual centering operation involves setting-up a dial indicator on the tool spindle, then rotating the same at a slow speed with a probe of the indicator tracing an internal surface of the bore, and centering the tool spindle by rotating a manually operated pulse generator until the swing of a pointer of the dial indicator disappears. Such centering operation is not only inefficient as taking a long time to perform, but cannot also be easily performed by unexperienced and unskilled operators.
In addition, the execution of the manual centering operation makes it impossible to return the tool spindle to a centering-start point where the tool spindle was before centering. This results in the unfortunate fact that feed errors that may have occurred in preceding operations of the machine tool cannot be detected even when a return of the tool spindle to a machine origin is executed in the tape mode for the purpose of detecting such feed errors.